The present invention relates to anti-C5 antibodies and methods of using the same. The complement system plays a central role in the clearance of immune complexes and in immune responses to infectious agents, foreign antigens, virus-infected cells and tumor cells. There are about 25-30 complement proteins, which are found as a complex collection of plasma proteins and membrane cofactors. Complement components achieve their immune defensive functions by interacting in a series of intricate enzymatic cleavages and membrane binding events. The resulting complement cascades lead to the production of products with opsonic, immunoregulatory, and lytic functions.
Currently, it is widely accepted that the complement system can be activated through three distinct pathways: the classical pathway, the lectin pathway, and the alternative pathway. These pathways share many components, and while they differ in their initial steps, they converge and share the same terminal complement components (C5 through C9) responsible for the activation and destruction of target cells.
The classical pathway is normally activated by the formation of antigen-antibody complexes. Independently, the first step in activation of the lectin pathway is the binding of specific lectins such as mannan-binding lectin (MBL), H-ficolin, M-ficolin, L-ficolin and C-type lectin CL-11. In contrast, the alternative pathway spontaneously undergoes a low level of turnover activation, which can be readily amplified on foreign or other abnormal surfaces (bacteria, yeast, virally infected cells, or damaged tissue). These pathways converge at a point where complement component C3 is cleaved by an active protease to yield C3a and C3b.
C3a is an anaphylatoxin. C3b binds to bacterial and other cells, as well as to certain viruses and immune complexes, and tags them for removal from the circulation (the role known as opsonin). C3b also forms a complex with other components to form C5 convertase, which cleaves C5 into C5a and C5b.
C5 is a 190 kDa protein found in normal serum at approximately 80 μg/ml (0.4 μM). C5 is glycosylated with about 1.5-3% of its mass attributed to carbohydrate. Mature C5 is a heterodimer of 115 kDa α chain that is disulfide linked to 75 kDa β chain. C5 is synthesized as a single chain precursor protein (pro-C5 precursor) of 1676 amino acids (see, e.g., U.S. Pat. Nos. 6,355,245 and 7,432,356). The pro-C5 precursor is cleaved to yield the β chain as an amino terminal fragment and the α chain as a carboxyl terminal fragment. The alpha chain and the beta chain polypeptide fragments are connected to each other via a disulfide bond and constitute the mature C5 protein.
Mature C5 is cleaved into the C5a and C5b fragments during activation of the complement pathways. C5a is cleaved from the α chain of C5 by C5 convertase as a amino terminal fragment comprising the first 74 amino acids of the α chain. The remaining portion of mature C5 is fragment C5b, which contains the rest of the α chain disulfide bonded to the β chain. Approximately 20% of the 11 kDa mass of C5a is attributed to carbohydrate.
C5a is another anaphylatoxin. C5b combines with C6, C7, C8 and C9 to form the membrane attack complex (MAC, C5b-9, terminal complement complex (TCC)) at the surface of the target cell. When sufficient numbers of MACs are inserted into target cell membranes, MAC pores are formed to mediate rapid osmotic lysis of the target cells.
As mentioned above, C3a and C5a are anaphylatoxins. They can trigger mast cell degranulation, which releases histamine and other mediators of inflammation, resulting in smooth muscle contraction, increased vascular permeability, leukocyte activation, and other inflammatory phenomena including cellular proliferation resulting in hypercellularity. C5a also functions as a chemotactic peptide that serves to attract granulocytes such as neutrophils, eosinophils, basophils and monocytes to the site of complement activation.
The activity of C5a is regulated by the plasma enzyme carboxypeptidase N that removes the carboxy-terminal arginine from C5a forming C5a-des-Arg derivative. C5a-des-Arg exhibits only 1% of the anaphylactic activity and polymorphonuclear chemotactic activity of unmodified C5a.
While a properly functioning complement system provides a robust defense against infecting microbes, inappropriate regulation or activation of complement has been implicated in the pathogenesis of a variety of disorders including, e.g., rheumatoid arthritis (RA); lupus nephritis; ischemia-reperfusion injury; paroxysmal nocturnal hemoglobinuria (PNH); atypical hemolytic uremic syndrome (aHUS); dense deposit disease (DDD); macular degeneration (e.g., age-related macular degeneration (AMD)); hemolysis, elevated liver enzymes, and low platelets (HELLP) syndrome; thrombotic thrombocytopenic purpura (TTP); spontaneous fetal loss; Pauci-immune vasculitis; epidermolysis bullosa; recurrent fetal loss; multiple sclerosis (MS); traumatic brain injury; and injury resulting from myocardial infarction, cardiopulmonary bypass and hemodialysis (see, e.g., Holers et al., Immunol. Rev. 223:300-316 (2008)). Therefore, inhibition of excessive or uncontrolled activations of the complement cascade can provide clinical benefits to patients with such disorders.
Paroxysmal nocturnal hemoglobinuria (PNH) is an uncommon blood disorder, wherein red blood cells are compromised and are thus destroyed more rapidly than normal red blood cells. PNH results from the clonal expansion of hematopoietic stem cells with somatic mutations in the PIG-A (phosphatidylinositol glycan class A) gene which is located on the X chromosome. Mutations in PIG-A lead to an early block in the synthesis of glycosylphosphatidylinositol (GPI), a molecule which is required for the anchor of many proteins to cell surfaces. Consequently, PNH blood cells are deficient in GPI-anchored proteins, which include complement-regulatory proteins CD55 and CD59. Under normal circumstances, these complement-regulatory proteins block the formation of MAC on cell surfaces, thereby preventing erythrocyte lysis. The absence of the GPI-anchored proteins causes complement-mediated hemolysis in PNH.
PNH is characterized by hemolytic anemia (a decreased number of red blood cells), hemoglobinuria (the presence of hemoglobin in urine, particularly evident after sleeping), and hemoglobinemia (the presence of hemoglobin in the bloodstream). PNH-afflicted individuals are known to have paroxysms, which are defined here as incidences of dark-colored urine. Hemolytic anemia is due to intravascular destruction of red blood cells by complement components. Other known symptoms include dysphasia, fatigue, erectile dysfunction, thrombosis and recurrent abdominal pain.
Eculizumab is a humanized monoclonal antibody directed against the complement protein C5, and the first therapy approved for the treatment of paroxysmal nocturnal hemoglobinuria (PNH) and atypical hemolytic uremic syndrome (aHUS) (see, e.g., Dmytrijuk et al., The Oncologist 13(9):993-1000 (2008)). Eculizumab inhibits the cleavage of C5 into C5a and C5b by C5 convertase, which prevents the generation of the terminal complement complex C5b-9. Both C5a and C5b-9 cause the terminal complement-mediated events that are characteristic of PNH and aHUS (see also, WO 2005/074607, WO 2007/106585, WO 2008/069889, and WO 2010/054403).
Several reports have described anti-C5 antibodies. For example, WO 95/29697 described an anti-C5 antibody which binds to the α chain of C5 but does not bind to C5a, and blocks the activation of C5, while WO 2002/30985 described an anti-C5 monoclonal antibody which inhibits C5a formation. On the other hand, WO 2004/007553 described an anti-C5 antibody which recognizes the proteolytic site for C5 convertase on the α chain of C5, and inhibits the conversion of C5 to C5a and C5b. WO 2010/015608 described an anti-C5 antibody which has an affinity constant of at least 1×107 M−1.
Antibodies (IgGs) bind to neonatal Fc receptor (FcRn), and have long plasma retention times. The binding of IgGs to FcRn is typically observed under acidic conditions (e.g., pH 6.0), and it is rarely observed under neutral conditions (e.g., pH 7.4). Typically, IgGs are nonspecifically incorporated into cells via endocytosis, and return to the cell surfaces by binding to endosomal FcRn under the acidic conditions in the endosomes. Then, IgGs dissociate from FcRn under the neutral conditions in plasma. IgGs that have failed to bind to FcRn are degraded in lysosomes. When the FcRn binding ability of an IgG under acidic conditions is eliminated by introducing mutations into its Fc region, the IgG is not recycled from the endosomes into the plasma, leading to marked impairment of the plasma retention of the IgG. To improve the plasma retention of IgGs, a method that enhances their FcRn binding under acidic conditions has been reported. When the FcRn binding of an IgG under acidic conditions is improved by introducing an amino acid substitution into its Fc region, the IgG is more efficiently recycled from the endosomes to the plasma, and thereby shows improved plasma retention. Meanwhile, it has also been reported that an IgG with enhanced FcRn binding under neutral conditions does not dissociate from FcRn under the neutral conditions in plasma even when it returns to the cell surface via its binding to FcRn under the acidic conditions in the endosomes, and consequently its plasma retention remains unaltered, or rather, is worsened (see, e.g., Yeung et al., J Immunol. 182(12): 7663-7671 (2009); Datta-Mannan et al., J Biol. Chem. 282(3):1709-1717 (2007); Dall'Acqua et al., J. Immunol. 169(9):5171-5180 (2002)).
Recently, antibodies that bind to antigens in a pH-dependent manner have been reported (see, e.g., WO 2009/125825 and WO 2011/122011). These antibodies strongly bind to antigens under the plasma neutral conditions and dissociate from the antigens under the endosomal acidic conditions. After dissociating from the antigens, the antibodies become capable once again of binding to antigens when recycled to the plasma via FcRn. Thus, a single antibody molecule can repeatedly bind to multiple antigen molecules. In general, the plasma retention of an antigen is much shorter than that of an antibody that has the above-mentioned FcRn-mediated recycling mechanism. Therefore, when an antigen is bound to an antibody, the antigen normally shows prolonged plasma retention, resulting in an increase of the plasma concentration of the antigen. On the other hand, it has been reported that the above-described antibodies, which bind to antigens in a pH-dependent manner, eliminate antigens from plasma more rapidly than typical antibodies because they dissociate from the antigens within the endosomes during the FcRn-mediated recycling process. WO 2011/111007 also described computer modeling analysis showing that an antibody with pH-dependent binding directed against C5 could extend antigen knockdown.